The document discusses the capabilities of new generation near-infrared (NIR) systems for analyzing grains and flours. It describes how newer NIR systems using photodiode arrays can more accurately measure additional quality parameters beyond just protein, moisture and ash contents, such as gluten content, water absorption, and starch damage. This allows millers to better optimize flour production processes in real-time without waiting for lab results.

1. T
he latest generation of near-infrared
systems for online measurements in
grain, flour and semolina open up
new possibilities regarding gluten,
water absorption and starch damage.
These allow millers to optimise flour
production directly and individually.
The grain processing industry has
been using the near-infrared system
(NIR) to continuously monitor the contents of raw, intermediate
and end products for years. More and more companies are now
using the advantages NIR technology offers for optimising
processes in real time.
NIR analysis makes it possible to assure consistent product
quality, and it makes a substantial contribution to the profitability
of a mill.
The evolution of the NIR machine ultimately means that
previous temporal restrictions and expenditures associated with
laboratory tests and raw materials are a thing of the past.
New generation of NIR
The first generation of NIR equipment focused on analysing
protein content, moisture and ash. These parameters were and are
the ‘classics’ of most online systems.
In addition, however, there are other quality parameters that
require compliance by the mills. For example, in wheat flour the
amount of gluten, the flour’s ability to absorb water, or the extent
to which the starch has been damaged, are important factors.
Older generations of online NIR systems were only able to
determine these parameters with insufficient accuracy and
reproducibility. By employing photodiode arrays (diode array,
DA), as in Bühler’s NIR Multi Online Analyzer MYRG, the
latest generation of NIR systems offers new possibilities for such
additional parameters and thus new potential for millers.
The NIR Multi Online Analyser MYRG is further
distinguishable by its durability and reliability, a claim reinforced
by some of its new features. The compact measurement probes of
the latest generation NIR are suited to the retrofitting of existing
production systems and it is the only probe actually located in the
production environment.
The control cabinet with its centralised spectrometer provides
ideal protection of the optical and electronic components.
There is also the possibility to add a probe for colour and speck
measurement to the same centralised system
The real time monitoring aspect is one of the major advantages
of Bühler’s new NIR system. The NIR units are extremely easy to
use once they are calibrated. Anyone can do measurements with
NIR units, compared to traditional reference method in the lab,
where a trained chemistry technician is needed.
Immediate corrective action is thus applied to the ongoing
production process without the need to wait for laboratory value,
giving you protein, ash, and moisture values in a matter of a few
seconds.
These additional calibrations eliminate long periods of waiting
for laboratory results and correctional measures can be performed
without delay, while simultaneously driving down costs
Possibilities for NIR
Near-infrared spectroscopy is very well suited for determining
the dominant contents in organic materials such as food and
feed products. But to do so, an NIR system needs not only good
hardware in order to function reliably, but a good mathematical
model (calibration) to determine the properties of an unknown
product.
The most important and NIR-active biochemical components,
such as water, starch, protein and fat, can be modeled (or
calibrated) without difficulty. However, other physical or
biochemical product properties can also be correlated with the
can do (almost) anything
Possibilities of modern NIR systems as exemplified by Bühler’s Multi Online Analyser MYRG
by Thomas Ziolko, Marketing and Product Manager, Grain Milling, Bühler
and Juste Hahne, Chemometrics, Grains & Food Automation, Bühler
54 | February 2016 - Milling and Grain
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2. NIR spectra as long as they are dependent on the combination of
the dominant contents and other properties such as particle size
distribution.
An example of this is the ability of flour to absorb and retain
water during the making of dough. The ability to absorb water
depends on the volume and quality of the protein, the condition
of the starch grains and the particle size distribution, among other
things.
Limits of NIR
Only those characteristics which actually leave information
in the NIR spectra and correlate with them can be calibrated.
An example of this is the so-called “sample” which is used to
evaluate the activity of certain enzymes in the flour.
NIR technology is only conditionally suited for lower ranges of
concentration. It is technically impossible to calibrate enzymes
for NIR because it takes only few ppm enzymes in the flour to
become active.
For generating NIR calibrations, the breadth of data is decisive
for accuracy and the sturdiness of the model. Models can only
predict products if their characteristics have already been
included in the model itself.
On the one hand, it is essential to cover the entire range of
features that are to be measured because the models are not
allowed to extrapolate. On the other hand, any disturbance
factors, such as specific product characteristics (particle size,
temperatures, source, chemical composition), the instrumentation
used and the surroundings, must also be taken into consideration
along with the characteristics which are supposed to be measured.
For the best calibration, several hundred samples can easily
become necessary under these conditions.
The future of NIR
Currently NIR is not a method for trace analysis and many
believe it would be beneficial to be able to measure parameters in
ppm or ppb concentration.
More importantly, perhaps, is the notion that every NIR unit
needs a calibration to get quantitative and qualitative results. The
calculation of such a calibrations is based on chemometric software
tools which needs resources and expert knowhow to be used.
Process
In order to compare spectra and samples, data must
be prepared and calculated using certain algorithms
(chemometry). The preparation of the spectra data using
various mathematical functions depends on the product itself
Table 1
Wheat Flour
Parameters
Reference Method Range Target SEP
Moisture TGA 701 @130°C 7 – 16 % 0.20 %
Protein Dumas / Kjeldahl 8 – 23 %dm 0.25 %
Ash TGA 701 @900°C
0.3 – 0.9 % dm 0.03 %
0.9 – 2.5 % dm 0.05 %
Wet gluten ICC 137 18 – 47 %mb14% 0.7 %
Water absorption
Brabender
Farinogram
47 – 85 %mb14% 1.0 %
Starch damage
Chopin SDmatic
AACC 76-33
5 – 31 UCD 1.0 UCD
Sandstedt &
Mattern
AACC 76-30
3.5 – 17 % 0.8 %
Milling and Grain - February 2016 | 55
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3. as well as the hardware being used and is necessary for better
separation of the interesting information (such as the protein
contents) from the uninteresting information (such as particle
size distribution).
Various possibilities exist which fall under the skill set of
chemometricians. The quantitative calibration models are usually
calculated with the PLS (partial least squares) algorithm which
searches for the largest differences in spectra and links these with
the characteristics to be calibrated.
NIR systems at work
The accuracy of an online NIR measurement system is usually
indicated by SEP (standard error of prediction). SEP is a random
standard error which is found between the reference laboratory
and the online measurement during at least 20 validation
measurements.
The random error in NIR (SEP) cannot be smaller than the
random error of the lab (SEL) since the calibration is based
on the data from the reference laboratory. For inhomogeneous
samples, where taking a representative sampling is already a large
problem, an online NIR measurement can be significantly more
accurate simply because of the size of the sample volume.
NIR devices require constant adjusting. First, the hardware (i.e.,
the light source, measuring window) must be frequently checked,
and secondly, the NIR calibrations themselves also need regular
monitoring and expanding since the product can undergo a natural
change in an unknown direction after a certain amount of time.
One of the main differences in the Multi NIR concept is that
there is one centralised spectrometer onto which can be added up
to six probes, allowing for NIR measurement in various places
throughout a mill.
QUALITY PARAMETERS
Gluten
The protein content in wheat flour consists of 90 percent gluten
(gluten protein). The important proteins in gluten are gliadin
and glutenin in equal portions. Gluten is a more or less flexible-
elastic substance which results when wheat flour dough is
allowed to rise.
In other words, it is essentially soaked gliadin and glutenin.
Since a higher protein content does not always mean a higher
content of gluten, an NIR calibration of gluten can offer a high
added value.
The gluten contents of wheat flour and its texture are a decisive
determinant of the dough’s behavior during kneading and baking.
In general: The higher the gluten content, the greater the water
absorption, the gas-retention ability and the expected volume of
baked product. Good gluten values: 30–34 percent.
The reproducibility of lab measurements is 0.4. With the NIR
Multi Online Analyzer MYRG, 0.7 is achieved.
Starch damage
‘Starch damage,’ from a scientific point of view, refers to
mechanically deformed starch.
Compared to intact starch, mechanically deformed starch can
absorb five times more water. That makes it the most important
factor in water absorption for flour and dough yield besides the
protein content.
Starch damage occurs during the various passages in the
milling process. If the technologist knows the desired degree of
starch damage they can adjust the grinding process according to
expectations, for example, by dimensioning the roll lengths (the
longer, the higher the starch damage) or the grinding pressure.
The reproducibility of lab measurements is 0.7. With the NIR
Multi Online Analyzer MYRG, 0.8 is achieved.
Water absorption
Water absorption [%] is the amount of water which must be
added to a flour in order to achieve a fixed dough consistency of
500 farinograph units (FU). For determining the water absorption
capacity, the farinograph from the Brabender company is
frequently used in the laboratory.
Industrial bakeries need raw materials of consistent quality so
that the process doesn’t need constant adjustment. This includes
the water absorption capacity of the flour.
The water absorption capacity is important for proper dough
preparation and controlling the dough during the rising and
baking process, among other things. So naturally, the amount of
water which is added in the baking process will depend on the
water absorption capacity.
There are possible corrective measures that a miller can
undertake: Adjusting the grinding process, performing various
types of conditioning, or adding attrition flour when the water
absorption is too low.
The reproducibility of lab measurements is 0.8, with the NIR
Multi Online Analyzer MYRG, 1.0 is achieved.
Accuracy
Table 1 summarizes the accuracy of the various calibration
systems which are available with the Bühler NIR Multi Online
Analyzer MYRG. A comparison of the SEP values with the
accuracies of the lab methods shows that the newest generation
of NIR spectrometers can determine additional parameters in
continuous production with amazing accuracy.
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